JP6071834B2 - Flux for single-sided submerged arc welding - Google Patents

Description

  The present invention relates to a flux used for single-sided submerged arc welding performed using one or two or more electrodes. More specifically, the present invention relates to a bead appearance improving technique in a single-sided submerged arc welding flux containing iron powder.

  In single-sided submerged arc welding, a flux to which iron powder is added is usually used in order to ensure the amount of welding and realize stable bead formation even in high heat input welding (for example, Patent Documents 1 and 2). reference.). However, the conventional single-sided submerged arc welding flux containing iron powder as described in Patent Document 1 has a problem that minute iron particle projections are likely to be generated on the surface of the front bead. Moreover, even when it is set as the flux composition described in patent document 2, an iron grain protrusion cannot fully be suppressed.

  Such protrusions on the surface bead are an obstacle in the painting process. For example, in the shipbuilding field, the International Maritime Organization has established coating standards for the ballast tanks of all ships and the double side of bulk carriers for the purpose of extending the life of the hull and facilitating maintenance. Revisions have been made to define the requirements for the removal of things that hinder paintability, such as spatter and bead surface contamination that occur during welding. For this reason, in the ship construction process, a grinder process is forced over the entire bead line in order to remove the iron grain protrusions.

  Therefore, conventionally, techniques for suppressing the generation of iron grain protrusions in a single-sided submerged arc welding flux have been proposed (see Patent Documents 3 and 4). For example, in the single-sided submerged arc welding flux described in Patent Document 3, bead soundness is achieved by setting the particle size and apparent density within a specific range. Moreover, in the bond flux for submerged arc welding described in Patent Document 4, the content of Fe component is restricted to 5% by mass or less in order to suppress the generation of iron grain protrusions.

Japanese Patent Laid-Open No. 11-267883 JP 2000-107885 A JP-A-6-277878 JP 2006-272348 A

  However, as in the technique described in Patent Document 3, simply controlling the particle size and apparent density of the flux has little effect on suppressing the generation of iron grain protrusions. In addition, when the Fe content is regulated as in the bond flux for submerged arc welding described in Patent Document 4, it is difficult to ensure a sufficient amount of welding in thick plate joining, and in high heat input welding. The bead shape deteriorates. Thus, in conventional bead appearance improvement technology, in single-sided submerged arc welding, while maintaining the effect of adding iron powder to the flux, the occurrence of iron grain protrusions is suppressed and the bead appearance is soundened. Not in.

  Therefore, the main object of the present invention is to provide a single-sided submerged arc welding flux capable of obtaining a sound front bead shape and mechanical performance.

In order to solve the above-described problems, the present inventors have conducted extensive experiments to ensure the soundness of the front bead in single-sided submerged arc welding using one or more electrodes. As a result, the present inventors controlled the particle size of the iron powder contained in the flux to suppress the occurrence of iron grain protrusions, and at the same time, “MgO amount + Al ₂ O ₃ amount + TiO ₂ amount” with respect to the iron powder amount. The inventors have found that it is effective to make it more than the amount, and have reached the present invention.

That is, the single-sided submerged arc welding flux according to the present invention is at least one selected from the group consisting of Si, Si alloys and Si oxides (SiO ₂ equivalent value): 6 to 12% by mass in total, CaO: 3 to 9 wt%, MgO: 15 to 35 _wt%, TiO 2: 5 to 23 _wt%, CaF 2: 2 to 10 _{wt%, Al} 2 O 3: _{5~23 wt%,} CO 2: 2 to 9 wt% , Na ₂ O: 0.5 to 3 mass%, B ₂ O ₃ : 0.1 to 1 mass%, Mo: 0.2 to 1 mass%, iron powder: 10 to 30 mass%, and Mn : 0.9 mass% or less, Ti: 1 mass% or less, Al: 3 mass% or less, the composition ratio of iron powder having a particle size of 300 μm or less in the iron powder is 90 mass% or more, and The content (mass%) of MgO is [MgO], and the content (mass%) of Al ₂ O ₃ is _[Al 2 _O 3], the content of TiO ₂ (% by mass) _[TiO 2], and when the content of iron powder (mass%) and [Fe], satisfies the following formula (I) .

In the single-sided submerged arc welding flux of the present invention, the particle size of the iron powder is controlled, and “MgO content + Al ₂ O ₃ content + TiO ₂ content” with respect to the iron powder content is set to a certain amount or more. As a result, in the temperature range where the weld bead solidifies, the settling rate of the iron particles is suppressed because the particle size of the iron particles is small, and the settling amount of the iron particles is also low because the content of the iron particles is relatively small. It is suppressed. Furthermore, it is possible to generate actively into the slag for example _{Mg 2 TiO 4, MgAl 2 O} 4 and Mg · Al · Ti-based oxides such as those solid solutions. Since the Mg, Al, Ti-based oxides are generated in the slag, the iron particles in the slag are bonded to these oxides before falling and adhering to the solidified bead surface. The formation of protrusions is suppressed.

This flux may contain 0.1 to 1% by mass of Ti.
Moreover, this flux may contain Mn in the range of 0.1-0.9 mass%.

  According to the present invention, since the flux component and its content are specified, even in single-sided submerged arc welding using one electrode or multiple electrodes, a sound bead shape and mechanical performance can be obtained regardless of the backing structure. Can be obtained.

It is an assumption figure of the iron particle generation behavior in the single-sided submerged arc welding process. It is sectional drawing which shows the groove shape of the steel plate used in the Example of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

  FIG. 1 is an assumption diagram of iron particle generation behavior in a single-sided submerged arc welding process. As shown in FIG. 1, in the single-sided submerged arc welding, when the flux 3 containing the conventional iron powder 5 is used, the iron powder 5 aggregates in the flux (slag) 4 during melting and solidification (of the iron powder). Aggregation 6), when this agglomerated iron powder (iron particles) 7 settles down and adheres to the surface of weld metal 2 (bead surface 2a) formed at the welded portion of base material 1 to generate minute protrusions. is assumed. Therefore, the present inventors have decided to solve the problem of iron grain protrusion generation by improving the characteristics of the flux.

Specifically, the flux according to the embodiment of the present invention is used for single-sided submerged arc welding, and at least one selected from the group consisting of Si, Si alloys, and Si oxides, CaO, MgO. , TiO ₂ , CaF ₂ , Al ₂ O ₃ , CO ₂ , Na ₂ O, B ₂ O ₃ , Mo and iron powder are contained in specific amounts, and Mn, Ti and Al are regulated to a specific amount or less. .

Moreover, in this flux, in the iron powder contained in the flux, the constituent ratio of the iron powder having a particle size of 300 μm or less is controlled to 90% by mass or more, and each of the components is satisfied so as to satisfy the following formula (I). The content is adjusted. In the following formula (I), [MgO] is the content (mass%) of MgO, [Al ₂ O ₃ ] is the content (mass%) of Al ₂ O ₃ , and [TiO ₂ ] is the content of TiO ₂ . The amount (mass%), [Fe] is the content (mass%) of the iron powder.

  Hereinafter, the reasons for limiting the composition of the flux of this embodiment will be described.

[Total content of Si, Si alloy and Si oxide: 6 to 12% by mass]
Si, and Si alloys such as Fe-Si has a deoxidation action and reacts with the oxygen in the weld metal to produce a SiO _2, the SiO ₂ acts as a Nebayuizai and slag forming agent . In addition, Si oxide also acts as a slag building agent.

However, when the total content of Si, Si alloy and Si oxide exceeds 12% by mass in terms of SiO ₂ , the viscosity of the entire molten slag increases and the fluidity of the slag decreases. In the case of high-speed single-sided submerged arc welding, the front bead width does not widen and becomes unstable, so that undercut is likely to occur. Furthermore, iron particles are likely to be generated. On the other hand, when the total content of Si, Si alloy and Si oxide is less than 6% by mass in terms of SiO ₂ , the solidification temperature of the molten slag becomes too high, so that a good surface bead shape cannot be obtained.

Therefore, the total content of Si, Si alloy and Si oxide is 6 to 12% by mass in terms of SiO ₂ . In addition, the flux of this embodiment should just contain at least 1 sort (s) of Si, Si alloy, and Si oxide.

[CaO: 3 to 9% by mass]
CaO has the effect of reducing the viscosity of the molten slag, increasing the fluidity of the slag, and widening the surface bead width. However, if the CaO content exceeds 9% by mass, the solidification temperature of the molten slag becomes too high and the surface bead shape is impaired. On the other hand, when the CaO content is less than 3% by mass, the effect of increasing the fluidity of the molten slag cannot be obtained, and the surface bead width is insufficient, so that undercut is likely to occur. Therefore, the CaO content is 3 to 9% by mass.

[MgO: 15 to 35% by mass]
Similar to CaO described above, MgO has the effect of reducing the viscosity of the molten slag, increasing the fluidity of the slag, and widening the surface bead width. However, when the content of MgO is less than 15% by mass, the effect of increasing the fluidity of the molten slag cannot be obtained, the surface bead width is insufficient, and undercut is likely to occur.

  On the other hand, since MgO is a component having a high melting point, if it is added in an amount exceeding 35% by mass, the meltability of the entire flux is impaired, a stable bead cannot be secured, and a medium convex bead tends to be formed. Here, the “medium convex bead” means that the center portion of the front bead is convex with respect to the welding direction, which is one of the causes of poor coating. Therefore, in the flux of this embodiment, the MgO content is 15 to 35% by mass.

  In addition, it is preferable that MgO content shall be 20 mass% or more. Thereby, the fluidity | liquidity of molten slag can be improved and the surface bead shape can be further soundened.

[TiO ₂ : 5 to 23% by mass]
TiO ₂ is a particularly effective component for improving the slag peelability in single-sided welding. However, when the content exceeds 23% by mass, the wave of the front bead becomes rough. Further, TiO ₂ content of less than 5 wt%, can not be obtained the effect of improving the slag removability as described above, even iron particle is likely to occur. Therefore, the TiO ₂ content is 5 to 23% by mass.

[Al ₂ O ₃ : 5 to 23% by mass]
Al ₂ O ₃ is a neutral component and is an effective component for adjusting the viscosity of the slag and the solidification temperature. However, when the Al ₂ O ₃ content is less than 5% by mass, the viscosity of the slag and the solidification temperature are lowered, and the bead width becomes uneven. On the other hand, when Al ₂ O ₃ is added in excess of 23 mass%, the solidification temperature of the slag becomes too high and the beads are difficult to spread, and the bead shape becomes convex. Thus, _Al 2 _{O 3} content is 5 to 23 mass%.

[CaF ₂ : 2 to 10% by mass]
CaF ₂ is a component that improves the meltability of the entire flux, and is an indispensable component particularly in a welding method in which the flux must be melted in a short time and slag must be generated, such as single-sided submerged arc welding. . However, when the CaF ₂ content exceeds 10% by mass, the arc stability is degraded and arc breakage is likely to occur. On the other hand, when the CaF ₂ content is less than 2% by mass, the effect of improving the meltability of the flux cannot be obtained, and bead meandering occurs. Therefore, CaF ₂ content is 2-10 wt%.

_[CO 2: 2 to 9 wt%
CO ₂ is an effective component for suppressing the penetration of nitrogen into the weld metal and reducing the amount of diffusible hydrogen, and is added to the flux as a metal carbonate. However, when the CO ₂ content is less than 2% by mass, the amount of diffusible hydrogen in the weld metal becomes high, and the cold cracking resistance deteriorates. On the other hand, when the CO ₂ content exceeds 9% by mass, the amount of gas generated becomes excessive, and a pock mark is generated on the front bead. Accordingly, CO ₂ content is 2-9 wt%.

[Na ₂ O: 0.5-3 mass%]
Na ₂ O is a component necessary for ensuring arc stability. Specifically, when the Na ₂ O content is less than 0.5% by mass, the arc becomes extremely unstable, arc breakage occurs, and the bead shape and penetration become uneven. On the other hand, when the Na ₂ O content exceeds 3% by mass, the hygroscopic resistance is lowered and the low temperature cracking resistance is deteriorated. Thus, Na ₂ O content is 0.5 to 3 wt%.

[B ₂ O ₃ : 0.1 to 1% by mass]
B ₂ O ₃ is reduced during welding and exists as B in the weld metal, and effectively acts to ensure toughness. However, when the content of B ₂ O ₃ is less than 0.1% by mass, the effect is not sufficiently exhibited and the toughness is deteriorated. On the other hand, if the B ₂ O ₃ content exceeds 1% by mass, the strength becomes excessive and high temperature cracking occurs. _Accordingly, B 2 _{O 3} content is 0.1 to 1 mass%.

[Mo: 0.2 to 1% by mass]
Mo is an effective component for improving the hardenability, and is added to the flux in the form of an alloy such as Fe—Mo in addition to Mo alone. However, when the Mo content is less than 0.2% by mass, the structure of the weld metal becomes coarse and the toughness deteriorates. On the other hand, if Mo is added in excess of 1% by mass, the strength of the weld metal becomes excessive and high temperature cracking occurs. Therefore, the Mo content is 0.2 to 1% by mass.

[Iron powder: 10-30% by mass]
Iron powder is an essential additive component in a single-sided submerged arc that requires a large amount of deposited metal at a time. And when iron powder content is less than 10 mass%, while the effect which supplements the amount of welding metal cannot be acquired, since the apparent density of a flux becomes small, blowing-up resistance deteriorates. On the other hand, when iron powder is contained exceeding 30% by mass, the iron powder tends to aggregate in the flux during melting and solidification, and the amount of the aggregated iron powder settles, and iron particles adhere to the bead surface. It becomes easy to do. In addition, the apparent density of the flux increases and the bead width cannot be secured. Therefore, content of iron powder shall be 10-30 mass%.

[Ti: 1% by mass or less]
Ti is an effective component for reducing the amount of oxygen in the weld metal as in the case of Si and Si alloy described above, but this effect can be sufficiently achieved by adding Si and / or Si alloy. In the form of flux, Ti is not an essential component. Moreover, when Ti content exceeds 1 mass%, slag will seize on the bead surface and slag peelability will deteriorate. Therefore, the Ti content is restricted to 1% by mass or less.

  On the other hand, when Ti is contained in an amount of 0.1% by mass or more, a further deoxidizing effect of the weld metal is realized, and the toughness can be improved. Then, in the flux of this embodiment, Ti can be contained in the range of 0.1 to 1% by mass as necessary. In addition to Ti alone, Ti is added to the flux in the form of an alloy such as Fe—Ti.

[Mn: 0.9% by mass or less]
Mn, like Mo described above, has an effect of improving hardenability and is an effective component for improving strength and toughness. However, when the Mn content exceeds 0.9 mass%, slag is formed on the bead surface. Seizure and slag peelability deteriorate. Moreover, in the flux of this embodiment, Mo is added, and thereby the effect of hardenability is obtained, so the Mn content is restricted to 0.9% by mass or less.

  On the other hand, when Mn is contained in an amount of 0.1% by mass or more, further improvement in hardenability is realized and toughness is improved. Therefore, in the flux of the present embodiment, Mn can be contained in the range of 0.1 to 0.9% by mass as necessary. Mn is added to the flux in the form of an alloy such as Fe-Mn in addition to Mn alone.

[Al: 3% by mass or less]
Al is an effective component for improving the toughness by refining the structure of the weld metal. However, since this effect can be sufficiently achieved by adding other components, Al is not an essential component in the flux of the present embodiment. On the other hand, if the Al content exceeds 3% by mass, quenching becomes excessive, the strength increases, and low temperature cracking occurs. Therefore, the Al content is restricted to 3% by mass or less. In order to refine the structure of the weld metal, the lower limit concentration is preferably 0.005% by mass or more, more preferably 0.01% by mass or more.
In addition to Al alone, Al is added to the flux in the form of an alloy such as Fe—Al or Al—Mg.

[Relationship between composition ratio of iron powder having particle diameter of 300 μm or less in iron powder, MgO content, Al ₂ O ₃ content, TiO ₂ content, and iron powder content]
In the flux of this embodiment, the composition ratio of the iron powder having a particle size of 300 μm or less is set to 90% by mass or more in the iron powder contained in 10 to 30% by mass. Here, “iron powder having a particle size of 300 μm or less” means screening of iron powder using a sieve having an opening of 300 μm based on JIS Z8801 (test sieve) according to a method in accordance with JIS Z8815 (general rule of screening test). This means the iron powder that passed through the sieve. Therefore, the lower limit of the particle diameter in “iron powder having a particle diameter of 300 μm or less” is not particularly limited. For example, among the iron powder having a particle size of 300 μm or less used, as the iron powder having a smaller particle size, screening of the iron powder is performed using a sieve having an opening of 45 μm based on JIS Z8801 by a method based on JIS Z8815. When performed, it is preferable that the composition ratio of the iron powder (iron powder having a particle size of 45 μm or less) that has passed through the sieve is 60% by mass or less.
In the present embodiment, 90% by mass or more of iron powder having a particle size of 300 μm or less is used with respect to the total mass of the iron powder. The upper limit of the constituent ratio of the “iron powder with a particle size of 300 μm or less” with respect to the total mass of the iron powder is not particularly limited, and for example, the constituent ratio can be 90% by mass or more and 100% by mass or less.
Further, in the flux of the present embodiment, the content of each component is in the above-described range, and ([MgO] + [Al ₂ O ₃ ] + [TiO ₂ ]) / [Fe] ≧ in the above formula (I) The MgO content, Al ₂ O ₃ content, TiO ₂ content, and iron powder content are adjusted so as to satisfy 2.5.

By defining the total of MgO content, Al ₂ O ₃ content, and TiO ₂ content with respect to the composition of iron powder and the iron powder content as described above, the iron particles can be solidified in the temperature range where the weld bead solidifies. The sedimentation rate is suppressed, and the amount of iron particles settled is also suppressed. Furthermore, since the Mg · Al · Ti-based oxide is actively generated in the slag, the iron particles in the slag combine with this oxide before falling and adhering to the solidified bead surface. There is an effect of suppressing the generation of microprojections on the bead surface. When both the above-described configuration of the iron powder and the relationship between the content ratios of the specific components are not satisfied, the amount of iron particles settled in the slag during welding increases. Therefore, in this case, microprojections are generated by dropping and adhering the iron particles in the slag to the solidified bead surface at a temperature near the solidification of the weld bead.
Therefore, the iron powder contained in the flux has a constituent ratio of particle size of 300 μm or less of 90% by mass or more and ([MgO] + [Al ₂ O ₃ ] + [TiO ₂ ]) / [Fe] ≧ 2. 5

[Other ingredients]
Components other than the above in the flux of the present embodiment are, for example, FeO, ZrO ₂ , and K ₂ O.

  As described in detail above, the flux of the present embodiment has been devised from the generation mechanism of microprojections, and the flux component and content are specified from a new viewpoint, so one electrode or multiple electrodes were used. Even in single-sided submerged arc welding, a sound bead shape and mechanical performance can be obtained regardless of the backing structure.

Specifically, the total content of Si, Si alloy, and Si oxide is 6 to 12% by mass, the composition ratio of iron powder having a particle size of 300 μm or less is 90% by mass or more, and ([MgO] + Since [Al ₂ O ₃ ] + [TiO ₂ ]) / [Fe] ≧ 2.5, it suppresses the aggregation of iron powder in the flux during melting and solidification and adhesion of the generated iron particles to the surface beads. can do. Thereby, in single-sided submerged arc welding, it is possible to form a sound surface bead having excellent mechanical properties and free from iron grain protrusions.

  The flux of this embodiment is mainly used in the single-sided submerged arc welding method, but the backing method is not particularly limited, and the flux copper back using the flux and copper as the backing material. This method, a flux backing method using only a flux as a backing material, and a backing method using a solid flux can be applied to any method. Further, the backing flux is not particularly limited, and a conventional flux can be applied as it is.

  Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. In this example, the steel plate shown in Table 1 and the wire shown in Table 2 are used, and the welding conditions shown in Table 3 below and the groove shape of the steel plate (base material 10) shown in FIG. The performance of each flux in the examples and comparative examples was evaluated. In addition, in a present Example, after mix | blending a raw material so that it may become a composition shown in the following Table 4 and Table 5, knead | mixing with a binder (water glass), it granulates, Furthermore, it is 400-650 degreeC using a rotary kiln. By baking and sizing, a flux having a particle size of 2.5 mm or less was obtained.

In addition, the remainder of the steel plate composition shown in the said Table 1 and the wire composition shown in the said Table 2 is Fe and an unavoidable impurity.
Further, “T.SiO ₂ ” shown in Table 4 and Table 5 above represents the total content of Si, Si alloy and Si oxide contained in the flux, and “MAT” represents MgO, Al ₂ O _3. , And the total content of TiO ₂ . Therefore, “MAT / Fe” shown in Tables 4 and 5 above is the ratio of the total content of MgO, Al ₂ O ₃ and TiO ₂ to the iron powder content (([MgO] + [A1 ₂ O ₃ ] + [TiO ₂ ]) / [Fe]).
Furthermore, in the column of “Iron powder composition” in Table 4 and Table 5 above, “A” represents that the composition ratio of iron powder having a particle size of 300 μm or less is 90% by mass or more based on the total mass of iron powder used. "B" represents that the constituent ratio of the iron powder having a particle size of 300 µm or less is less than 90 mass% with respect to the total mass of the iron powder.

  The evaluation of each flux in the examples and comparative examples is based on welding workability (bead appearance, undercut, etc.), ultrasonic flaw detection (UT) test based on JIS Z3060 (presence of cracks, slag entrainment, etc.) and JIS Z2242. The Charpy impact test was performed. The evaluation results are shown in Table 6 below.

  In the evaluation of welding workability shown in Table 6 above, the “iron grain protrusion” is a part where the iron powder contained in the flux melts and aggregates and adheres to the bead surface, which is a cause of coating failure. It becomes one of. In this example, a case where 100 or more iron particles having a particle diameter of 200 μm or more exist per 1 m of the bead length by observation of the bead surface was defined as “with iron particle protrusions”.

  Further, the “medium convex bead” means that the center portion of the front bead is convex with respect to the welding direction, which is one of the causes of poor coating. “Meandering protrusion” refers to a state in which convex protrusions meander, and is a kind of medium convex bead. “Slag seizure” means that the slag after welding is seized on the bead and is difficult to peel off, and the appearance of the bead after peeling is deteriorated, which is one of the causes of coating failure. “Undercut” is a kind of weld defect in which a base material is dug along the toe of welding and remains as a groove without being filled with the weld metal.

  “Rough wave” means that the total length of five consecutive pitches exceeds 40 mm, which is one of the causes of coating failure because the bead appearance deteriorates. “Bead irregularity” refers to the case where the difference between the maximum width and the minimum width of an arbitrary 50 mm bead exceeds 5.0 mm and is one of the causes of coating failure because the bead appearance deteriorates. Become. Details regarding “undercut”, “coarse wavy” and “bead irregularity” are described in “Appearance Test Passing Guidelines” established by the Japan Welding Association in March 1983.

  On the other hand, in the Charpy impact test, Charpy absorbed energy (vE-20 ° C) at a test temperature of -20 ° C passed 50J or more, and less than 50J was rejected.

  As shown in Table 6, the fluxes of Examples 1 to 18 produced within the scope of the present invention were good in all of welding workability, ultrasonic flaw detection (UT) test, and toughness (vE-20 ° C). It was.

  On the other hand, as shown in Table 6, since the total content of Si, Si alloy, and Si oxide was less than the lower limit of the range of the present invention, the flux of Comparative Example 1 generated an intermediate convex bead. On the other hand, in the flux of Comparative Example 2, since the total content of Si, Si alloy and Si oxide exceeded the upper limit of the range of the present invention, undercut and iron grain protrusion occurred. Moreover, since the CaO content of the flux of Comparative Example 3 was less than the lower limit of the range of the present invention, undercut occurred. On the other hand, the flux of Comparative Example 4 had a convex bead because the CaO content exceeded the upper limit of the range of the present invention.

The flux of Comparative Example 5 had an undercut because the MgO content in the flux was less than the lower limit of the range of the present invention. On the other hand, in the flux of Comparative Example 6, since the MgO content exceeded the upper limit of the range of the present invention, a medium convex bead was generated. Also, the flux in Comparative Example 7 is greater than the upper limit of the present invention range "T.SiO _2", since the content of TiO ₂ is less than the lower limit of the range of the present invention, the iron particle projection occurs, Mn content Since the upper limit of the range of the present invention was exceeded, slag seizure occurred. On the other hand, in the flux of Comparative Example 8, the TiO ₂ content exceeded the upper limit of the range of the present invention, so that the beads were rough.

Since the flux of Comparative Example 9 had an Al ₂ O ₃ content that was less than the lower limit of the range of the present invention, the bead width alignment was poor. On the other hand, in the flux of Comparative Example 10, the Al ₂ O ₃ content exceeded the upper limit of the range of the present invention, so that the beads became convex.

In the fluxes of Comparative Examples 11, 12, and 16, the relationship between MgO content, Al ₂ O ₃ content, TiO ₂ content and iron powder content is out of the scope of the present invention. Specifically, ([MgO] + [Al ₂ O ₃ ] + [TiO ₂ ]) / [Fe] ≧ 2.5 is not satisfied. For this reason, in the fluxes of Comparative Examples 11, 12, and 16, iron grain protrusions were generated on the bead surface.

  In the flux of Comparative Example 13, the composition ratio of the particle size of the iron powder was out of the range of the present invention, and as a result, the bulk density of the flux was increased, and as a result, an intermediate convex bead was generated.

  As for the flux of Comparative Examples 14 and 15, as a result of the amount of iron powder being out of the range of the present invention, the flux of Comparative Example 15 is further out of the range of the composition of the particle size of the iron powder, and the flux As a result of the increase in the bulk density, the beads became convex and the protrusions meandered.

  In addition, in the evaluation of each flux of the examples and comparative examples described above, single-sided submerged arc welding was performed using a backing material generated with a solid flux, but a flux copper backing method using a copper plate and a backing flux, and Similar results were obtained in the flux backing method performed while solidifying the backing flux without using a copper plate. Tables 4 and 5 show the results of three-electrode welding, but there is no difference in the melting and solidification process of the flux after welding in the case of one-electrode, two-electrode, and even four-electrode welding. The same results as in the three-electrode welding shown in Tables 4 and 5 were obtained.

  From the above results, it was confirmed that by using the flux of the present invention, a sound surface bead shape and mechanical characteristics can be obtained in single-electrode or multi-electrode single-sided submerged arc welding.

DESCRIPTION OF SYMBOLS 1, 10 Base material 2 Weld metal 2a Bead surface 3 Unmelted flux 4 Flux in melting and solidification (slag)
5 Iron powder 6 Aggregation of iron powder 7 Aggregated iron powder (iron particles)

Claims (3)

At least one selected from the group consisting of Si, Si alloy and Si oxide (in terms of SiO ₂ ): 6 to 12% by mass in total,
CaO: 3 to 9% by mass,
MgO: 15 to 35% by mass,
TiO _2: 5 to 23 wt%,
CaF ₂ : 2 to 10% by mass,
Al ₂ O _3: 5~23 wt%,
CO ₂ : 2 to 9% by mass,
Na ₂ O: 0.5 to 3 wt%,
B ₂ O ₃ : 0.1 to 1% by mass,
Mo: 0.2-1 mass%,
Iron powder: 10-30% by mass
And containing
Mn: 0.9 mass% or less,
Ti: 1% by mass or less,
Al: restricted to 3% by mass or less,
In the iron powder, the composition ratio of iron powder having a particle size of 300 μm or less is 90% by mass or more, and
The content of MgO (mass%) [MgO], the content of _Al 2 _{O 3 (mass%) [Al 2 O 3]} , the content of TiO ₂ (mass%) _[TiO 2], and iron powder A flux for single-sided submerged arc welding that satisfies the following formula (I) when the content (% by mass) of [Fe] is [Fe].

  The flux for single-sided submerged arc welding according to claim 1, containing 0.1 to 1% by mass of Ti.   The flux for single-sided submerged arc welding according to claim 1 or 2, comprising 0.1 to 0.9 mass% of Mn.

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